Conventionally, color cathode ray tubes are formed such that a face plate on which phosphors are coated and a shadow mask is mounted is connected to a funnel to form a bulb. An electron gun is inserted, exhausted and sealed in the neck of the bulb. The phosphors coated on the face plate thereof are formed in a series of patterns each having Red, Green, Blue(R,G,B). Electron beams emitted from the electron gun pass through the shadow mask and impact the phosphors thereby forming spots on a screen. However, whereas a plan for the color cathode ray tube is that the R.G.B. electron beams should each strike the corresponding R.G.B. phosphors, in practice some electron beams strike other neighbouring phosphors thereby causing mixed colors. To prevent such problem, a black matrix is formed among the R.G.B. phosphors, so that some electron beams do not misland on the neighbouring phosphors.
This black matrix is formed by a well-known photolithography. A photo sensitive material is deposited on the inner surface of the face plate. A prepared mask for black matrix is placed thereon, exposed to the light and then developed, thereby forming photo sensitive material stripes. On the remaining space formed therebetween is deposited the black matrix composition and then these stripes ar dissolved and removed by an etching solution thereby forming black matrix stripes.
However, these black matrix stripes should be in a straight line, and this depends wholly upon the straight line property of photo sensitive material during the photolithography process.
A method of obtaining the photo sensitive material having good straight line property has been studied. Recently, it was discovered that photo sensitive material comprising a polyvinylpyrrolidone as a main element has excellent photo sensitive straight line property by selecting and controlling a photo sensitive region. On the basis of this discovery Japanese Patent Publication (before Examination) No. Sho 63-72029 provides a method of improving the straight line property of the black matrix by adding polyvinylpyrrolidone thereto. However, even though this polyvinylpyrrolidone photo sensitive material has the excellent straight line property when exposed to light, it makes poor use of such property at the etching process.
To etch the polyvinylpyrrolidone type photo sensitive material after exposure to light, hydrogen peroxide water, a dilute sulfuric acid solution or a sulfamic acid solution is used as the etching solution. However, since the chemical property of polyvinylpyrrolidone is very stable, it has the disadvantage of remaining as a residue even after etching and attaching phosphors to this residue when depositing the phosphors thereby causes the mixed colors.